Apparatus for determining the concentration of a chemically active gas in an atmosphere



y 8 1952 M. CURRY 2,602,729

APPARATUS FOR DETERMINING THE CONCENTRATION OF A CHEMICALLY' ACTIVE GAS IN AN ATMOSPHERE 2 SHEETS-SHEET 1 Filed Dec. 20, 1946 July 8, 1952 '2,6o2,729

M. CURRY APP TUS FOR DETERMINING THE CONCENTRATION HEMICALLY ACTIVE GAS IN AN ATMOSPHERE Filed Dec. 20, l 2 Sl-lEETS-SI-IEET 2 WWW flag 7 m? Jim cmwwlaa Mu Patented July 8, 1952 UNITED STATES PATENT OFFICE APPARATUS FOR DETERIWINING THE CON- CENTRATION OF A CHEMICALLY ACTIVE GAS IN AN ATMOSPHERE Manfred Curry, Bruckton, Mass.

Application December 20, 1946, Serial No. 717,440

In Germany October 30, 1941 i 6 Claims. (Cl. 23255) This invention relates to a method of and apparatus for testing the concentration in an atmosphere of a gas or gases which are sufliciently 1 active chemically to cause some observable and measurable change in a substance exposed thereto. More particularly the invention relates to the testing of an atmosphere to determine quickly atmosphere is directed against some substance which is capablev of reacting with the oxidizing component of the atmosphereso as to be changed in some observable characteristic such as color. By standardizing the conditions under which the testing is performed, quantitative results can be obtained from the degree of colorchange. For example, in testing the concentration of QXidiu" ing gases such as ozone in an atmosphere, I can employ a solution of starch and an iodide such as potassium iodide, with the addition of suitable buffers such as phosphates to maintain the pH of the solution at a proper value. The oxidizing component'of the atmosphere which is directed against asurface or film-of such-mixture reacts :chemically with the iodide to form free iodine which actsonthestarch to turn it blue, the depth of the color thus formed being a function of the quantity of iodine thus released. r According to the invention, apparatus is provided whereby a stream of the atmosphere to be description thereof, and to the drawing, of which:

' Figure I isfla view partly in section and partly schematic of the apparatus designed t9 Perform the novel process of the invention;

of apparatus;

the line Figure 2 is a section on 2-2 of Figure 1;

Figure 3 is a section on the line 33 of Figure 1;

Figure {4' is a section on the line 4- 1 of Figure 1; l p

Figure 5 is a section on the line 5-5 of Figure 1;

Figure ,6 is a perspective view of the cover plate-of the apparatus;

Figure 7 is a perspective View of an absorbent pad used in the apparatus; i

Figure 8 is a schematic view of a modified form Figure 9 is a partial plan modified form of apparatus; V

Figure 10 is an elevational View of a portion of'the absorbent strip shownain' Figure 9jtogether with moistening means;

view of another ,Figure 11 is a section onthe line H -H of Figure 10; g t

Figure 12 shows a modified form of absorbent strip.

The apparatus shown in Figure 1 is designed to employ an absorbent pad in'the shape of a paperdisk 20' such as is illustrated in Figure '7. This disk is preferably divided into a convenient number of sectors by radial lines 22 of shellac or the like which form'non-absorbent barriers, between the absorbent sector areas of the disk. This disk maybe supported on an underlying disk 24 and a surrounding annulus 26, both of these supporting members being non-absorbent. The annulus 26 is in turn sup orted by a frame 30 which rests upon a collar 3 the latter being secured to a vertical shaft 3 the upper end of whichis threaded as at 36 to receive the small supporting disk 24 and a'c'ap screw 38 by which the central portion of the paper disk 20 can be clamped to the disk 26. As shown, a loose washer All may be inserted between the paper disk at and'the cap screw 33w Over the paper disk 20 is a plate 62 which may conveniently be thecover of a box 44 which may house most of the apparatus indicated in Figure 1, the box it itself being indicated bytwo short sectional fragments of its side walls. The box top is has a central aperture 45 concentric with the shaft 34. The box top is also preferably slidable in grooves on the box walls 44 so that the cover can be removed when it is desired to, replace a paper. disk 20. The box top 42 hasalso a smaller aperture 4b which is over a portion of the paper disknot far from its periphery. i

In practicing the process of the invention, one of the. absorbent sectors of the paper disk is moistened with a solution which is adapted to be discolored by oxidizing agent in the atmosphere to be tested. For example, a thin aqueous solution of starch and an iodide such as potassium iodide may be applied to the paper disk 20. The remainder of the disk is sealed from the atmosphere while a stream of atmosphere is directed against the freshly moistened area exposed through the aperture 46. This exposure to the atmosphere is maintained for a predetermined period of time which may "be measured by a suitable clock 56 or equivalent device. ,At the end of such period the paper disk 26 is lowered sufficiently to permit rotation thereof so as to bring the next absorbent sector beneath the aperture 46. The plate 26 is at once raised to press the paper disk against the top plate 42 and thus to seal the disk from the atmosphere with the exception of a central exposed portion which is neglected and the portion exposed through the aperture 46. This latter portion is thereupon moistened as hereinafter described and the process is repeated. After all or a desired number of the sectors have been moistened andexposed to a stream of the atmosphere, the disk is removed from the apparatus and dried. By colorimetric tests of the discolored portions of the diskfidete-rminations of the concentration :of oxidizing agents in the atmosphere can bereadily made. Forth-is purpose a, colorchart can be employed having a series of progressively deepening shades for matching with the discolored areas on the disk, the color chart being calibrated in terms of percentage of concentration of oxidizing agents in the atmosphere. or as hereinafter described, ,a photo-electric device may be used tomeas-ure the .depth of color of the discolored areas, this device being used with or without a recording device by which a record can be madaatfrequent intervals of the values obtained for the concentration of the oxidizin agents in the atmosphere.

Referring to Figure 1, the apparatus therein shown may comprise a suitable driving motor .66 which drives a fan .62 and .also .a shaft .64, t e latter being connected to themotor-through a suitable clutch 56 which. can be engaged and disengaged as hereinafter described. The .fan 62 y be n losed i a suitable blower housing 66 I which serves to direct a stream throu h a discharge opening 16 toward the apertureAB. Fig-- ure 1 shows the apparatus at the stage of a cycle of op r tions in which the pla e 26 which sup ports the pa er disk 26 has been lowered for the rotation of the disk and-th disk has just been advanced to bring the next successive beneath the aperture 46 so that the disk 26 ready to be lifted again against theunder surface of the t p pla e the paper disk a suitable camIZ may be proi ed s hown n Fi ure 3. this camheme mount-colon the shaft-.64. On the edge of this cam rides a cam follower L4, wh h is carr ed y a leg "I6 secured to the supporting frameso. In

actual construction. a sufficient numberof such legs I6 are provided, only one being indicated in Figure 1 to avoid confusion. When thencam'fol- .lower :14 moves onto'thei high portion of the cam ing elements are quickly-rotated througha suf- For the elevation of gears, 62 to the shaft 34, the step by step rotationof themember 80 bein controlled by a pin 84 which i mounted on a disk 86, the latter be The construction and operation of the Geneva movement is old and well understood.

"For the moistening of the absorbent sectors, a moistening pad 90 is reciprocally mounted in a suitable cylinder 92. The moistening pad is reciprooated by ,a cam follower 94 which bears on a cam ,96 mounted on the shaft. The moistening padBIl is saturated with'a suitable solution such as an aqueous solution .ofstarch with .an iodide andpreferably also with buffers such as phosphates, and is moved upward to engage the disk 26 through an aperture 98 .in.the p'1ate.;26

which is directly beneath the aperture 46 in the top plate 42. Asindicated in Figure 5,.the shape iofthe cam 96 provides .for an upward movement'of the pad atthe proper time, .followed at once by a'descending movement.

The operation of the parts .of the apparatus thus-far described maybe automatically controlled by electric circuits and switches suchas are illustrated in Figure 1. The clock mechanism so is constructed-to operate at predetermined intervals of "time a "suitable switch having amovable member which can be moved into contact with a switch element I62 or-a second switch element H14 in order to close one-or the other of two electric circuits. The clock elements can be adjusted to alter the time intervals as desired. Cooperating with the-switch I06 is a multiple switch consisting of bridging conductors'llfl, I12 and H4. These conductors are insulated from one another but may "be mounted on a common support rod H6 which is movable by-a cam follower II8 riding in a cam slot I 26, the cam wheel I22 being mounted on the shaft 64. Each of the bridging conductors I I0, I I2, and I I 4 is arranged to move into-and out of contact with a corresponding pair ofswitch contacts so that these bridging conductors are parts of three separate switches which are simultaneouslyoperated by movements of the support rod I I6. As indicated in Figure '1, when the rod H6 is lifted by its cam, the switches H0 and H2 are closed and the switch H4 is opened. Conversely when the rod I I 6 is lowered, the switches III) and H2 are opened and the switch I l-4 is closed.

The clutch 66 may be magnetically operated by means of a coil I26, this coil being in circuits controlled by the switches H2 and II4.

A cycle of operations of the apparatusthus far described is as follows. Starting with the "apparatus in the condition illustrated in Figures 1 to 5, inclusive, the paper disk 26 has just been rotated through an angle of 60, the switches I02, H6 and H2 are closed so that the motor is .operating and the clutch 66 is engaged. This means that the fan 62 is beingrotated as is also the cam shaft 64. It is evident from Figure "3 that the plate 26 is about to be :lifted to press the disk 26 against theunder face of thetop plate 42. When this has been dOneQcam "I22 'duit I311.

lowers the rod H6, thus simultaneously opening the switches H and H2 and closing the switch H4. The" opening of the switch I I2 breaks the circuit through the coil clutch I26, thus disconnecting the cam shaft 64 from the motor, and the opening of the switch H0 stops'the motor since the switch I04 is at that time open. The entire apparatus is now at rest and remains at rest until the clock work 50 shifts the switch arm' I00 to close the switch I04. Since the switch H4 is at that time closed, the closing of switch I04 starts the operation of the motor 50, and engages the clutch 66 so that the rotation of the shaftaBfl is resumed. This soon results in the elevation of the moistening pad!!!) to moisten the hole 46. The moistening pad at once descends and the camIZZ then operates the switches H0, H2 and I I4 .to the position shown in Figure .1. The opening of the switch -I I4 de-energizes the clutch coil I26 so that the clutch 66 becomes dis; engaged, thus stopping the shaft 6 The motor 60 however continues to operate the fan 52 so that a stream of atmosphere is directed through the japerture 46 against the moistened spot on -;thej- .-paper disk, this continuing .through a predetermined time interval measured by the clock 50. At the end of such interval the clock oper ates to open the switch I04 and close the switch I02. The latter causes the clutch 66 to engage and the shaft 64 to resume rotation. This rota tion soon causes the cam follower I4 (Figure3) to ride onto the low portion of the cam I2, thus lowering the plate 26 and the paper disk 20 sup ported thereon. The Geneva movement shown in Figure 4 thereupon operates to rotate the plate and disk a step, bringing the apparatus to the point of the cycle illustrated in Figure '1. By suitably setting the switchoperating elements of the clock 50 this cycle of operations can be made to repeat itself automatically in immediate su'ccession or at desired intervals. When it has been repeated six times, the apparatus is stopped; the paper disk, 20 removed and dried, the discolored parts being compared with a color chart to'determine the depth of color on the spots as a measure of the concentration of oxidizing agents in the atmosphere during the testing periods. A fresh paper disk 20 is inserted in the apparatus, whereupon the cycles can be resumed.

Since the color depth of the spots on the paper disk. depend on the rat of reaction of the solution with the oxidizing agents in the atmosphere to which it is exposed, and since such rate of reaction may depend in some measure on the temperature of the exposed surface, it is desirable to maintain the exposed surface'of the paperdisk at a substantially uniform temperature. This may be done by heating the air stream which is directed against the aperture 46. For this purpose an auxiliary stream of air may be supplied to the fan casing 63 through a conduit I30,

the air supplied through the .conduit I30 being purified, warmed and preferably moistened by apparatus schematically indicated in Figure 8.

A modified form of apparatus is indicated in Figure 8, this apparatus including a driving motor 60, a fan (52 within a fan housing Sit-which draws atmosphere from the space surrounding the fan housing and alsomixes with this stream an auxiliary stream introduced through a con- This auxiliary stream is first drawn through a filter I32 which may be in the form of a box containing activated charcoal which has the property of absorbing the oxidizing agents.-

portion of the paper disk which underlies the The air stream'from the filter p asses 'through'a humidifier I 34 where it is suitably moistened so of the mixture. In order to maintain a constant temperature at the moistened surface 'where the chemical reactions take place, the auxiliary air stream may be warmed by a heating unit I40 which is preferably controlled by a thermostat M2 placed in the mixed air stream at a point just'before it is discharged against the "moistened absorbent paper. Y

The apparatus indicated in Figure 8 is characterized by the use of a long strip I44 of paper instead of the disk 20; This strip is preferably supplied in a roll I 45, the strip being divided into separate absorbent areas by slots or non-absorbent areasl Figure 10 illustrates an absorbentpaper strip in which absorbent areas I40 are separated by transverse bands I 48 which are made non-absorbent by shellac or other suitable means. Figure 12 illustrates a strip in which absorbent areas I46 are separated by transverse slots I50 which extend part way across the strip, the connecting portions I52 and 15-4 being treated to make them non-absorbent. The connecting portion I54 is preferably of substantial'width to receive data such as the date and time of the tests made by means of the successiveabsorbent areas I45, and any other pertinent data'such' as significant events occurring at such times.

a As the paper strip- I44 is drawn from the supplyroll I45, the successive areas I46 are moistened by a'reciprocating pad 90which may be operated as hereinbefore described in connection with the mechanism shown in Figure 1, this pad being saturated with a solution of starch and an iodide to which may be added if desired buffers such as phosphates to maintain the pH number at a suitable constant value.

The freshly moistened area of the paper strip is moved into line with the stream of mixed air blown through the fan housing 5-8 and is held there for a predetermined interval of time after which the strip is again advanced so as to move the exposed area into a drier I and at the same time to move the next freshly moistened area opposite the discharge orifice of the fan housing 58. The drying apparatus may be of any suitable description as, for example, a housing into which is constantly introduced a stream of warm, purified air driven by a suitable fan I62 through a carbon filter I54 and heated'by heating unit .llitbefore it enters the drier housing. The dried absorbent areas which have been discolored by action of the oxidizing agents in the air streampass from the drier to a photo electric deviceby which the degree of color produced on 'each area is accurately measured. Devices of this kind are well known, one being schematically illustrated in Figure 8. This consists ofa lamp and lens unit I!!! for projecting abeam of light This unit maybe arranged to shine through the paper strip ormay be arranged on the other side to shine against it so that the photo-electric element II2 can'receive either transmitted light or reflected light. In either event the element is connected to a galvanometer I I4 having a dial I I6 preferably calibratedto read in terms of concentration of @the active agents in the atmosphere which is to' be tested. An index I18 cooperates with the dial to-iindicate .such concentration. In addition, a

recording index-element I Bitmay vbe provided with ing drum I82. Anysuitable means may beprovided forfeeding the paper strip I44 with astep by step movement. For example, feed rolls I84 are indicated, suchirolls being :driven by suitable means .such as a ratchet wheel I86 cooperating with a magnetically operated pawl I88. By apzparatus such as has been described, a continuous record of changesin concentration of oxidizing agents in an atmosphere can be made, the values of the concentration being noted-at regu= lar frequent intervals. 7 v

:A-nother modified form of apparatus is indicated in Figure 9. This comprises an absorbent paper strip I44 which may be divided into'separateabsorbent areas ME inthe mannerindicated in Figure 10 or in Figure 12. This paper is supplied .from a'roll I45 and isdr-awn at a constant .raterather thana step by step feedpasta moistening device I90. As indicated in Figures- 10 and 11,2this device may be in the form of a tube with a fine bore of sufi'iciently small diameter to raisesolution from a reservoir I 92 by capillarity. The end of this tube .bears lightly against'the strip M l so that solution is'absorbed. therefrom by the absorbent material of the, paper strip. To prevent the absorption ofanexcessive amount or" solution, the paper "strip may be treated with "shellac or other material capable of making it non-absorbentealongrportions of the path of contact of the-tube IS!) with the paper as illustrated in Figures 10 and 12. Thus as the paper .strip travels, thetube-engages absorbent surfaces for only briei intervals as at I94. In order to strengthen the stripand avoid breakage by feeding tension when it is weakened by being moistoned, abacking strip -2-1l0pf .cellophaneor-other suitable material may be joined to itfrom a conveniently located supply roll .202 to reinforce it. The strip I :14 upon being-moistened progresses past a fan 294 which blows atmosphere against it. As shown in Figure 9, the treated area is maintained at a substantially constant temperature by means of a heated block 206 against which it bears as it passes the fan .204. This blockis'heated by a unit 288 mounted therein and controlled. by a thermostatic element 2H3 also mounted in the block adjacent to the bearing surface. The strip I44 and its backing strip 200 are fed at a suitable rate to permit suflicient exposure of the moistened areas for reaction with 'theoxidizing agents in the atmosphere blown against-the moistened area. From the block 206 the-strip moves through a drier M2 which may besimilar to the dryingapparatus I511 shown-in Figures. -As-the strip emerges .from thedrier, afa-cing strip 2 I 4 of-cellophaneorother suitable transparent material may be joined thereto so that the strip is protected-on both faces. The

strip then-proceeds to anysuitable feeding and take-up mechanism (not shown) the color depth of the discolored areas being'measured and indi- .cated or .recorded ashereinbefore describedin connection with ,Figure- 8.

Iclaim:

-1, A unitary, electrically operated apparatus for automatically .determining and recording'the concentration of reactive agents in an atmosphere, which comprises an absorbent pad, an electrically driven'fan for directing a stream of "said atmosphere against said pad, electrically *jdriven means for moving said pad through .said

stream of atmosphere, thereby exposing the .surface or the pad thereto for -a pre-determined interval of time, capillary means for contacting said pad and moistening it with aliquid thatis reactiveto said reactive agents, said capillary means being-located in the path of travel of the pad prior and adjacent to its point of exposure to the stream of atmosphere, a drying chamber located'about the path of travel of the pad subsequentand adjacent to its point of exposure to the stream'of atmosphere, and means for supplying a'stream of hot, dry atmosphere'to said drye ingchamber, such means including anelectrical heating device and a filter located in the path of the stream.

2. apparatus as claimed in claim 1, wherein the driving means'for moving the absorbent pad operates :'at a constant speed, the capillary means is in continuous contact with the absorbent pad, and the absorbent pad passes over an electrically heated-block of metal while it is exposed to the stream oi. atmosphere. 7

3. An apparatusas claimed in claim '1, wherein the absorbent pad has a plurality of segregated areas-'andthe driving means for moving said pad includes a clock-work mechanism imparting intermittent motion thereto.

l; An apparatus as claimed in claim 3, wherein the capillary means consist of a solution saturated trick that intermittently contacts the absorbent pad and is reciprocated by the driving means for said absorbent pad. Y

5. A unitary, electrically operated apparatu for automaticallydetermining and recording the concentration of reactive agents in an atmosphere, which'comprises an absorbent pad, a first conduit including an electrically driven fan for directing a'stream of said atmosphere against said pad, said first conduit having an intake opening to the atmosphere and a second intake connected with a: second conduit containing electrical heating means and a filter, with thermostatically controlled valve means for regulating the proportions of atmosphere admitted through the two intakes, electrically driven means for moving said pad through said stream of atmosphere, thereby exposing the surface of the. pad thereto for apredetermined interval of time,;capillary means for contacting said pad and moistening it with a liquid that is reactive to said reactive agents, said capillary means being located in the path of travel of the pad prior and adjacent to its point of exposure to' the stream MANERED CURRY.

REFERENCES crrsn The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Dieterich Jan. 14, 1902 Smyly July 13,1915

Number (Other references on following page) Number Number FOREIGN PATENTS Country Date Great Britain Sept. 3, 1903 Great Britain Dec. 16, 1915 Great Britain Dec. 1, 1927 Great Britain Aug. 10, 1933 Great Britain Nov. 2, 1938 OTHER REFERENCES Lunge, Technical Gas Analysis, pages 219,

220, Van Nostrand and 00.. 1914. 

1. A UNITARY, ELECTRICALLY OPERATED APPARATUS FOR AUTOMATICALLY DETERMINING AND RECORDING THE CONCENTRATION OF REACTIVE AGENTS IN AN ATMOSPHERE, WHICH COMPRISES AN ABSORBENT PAD, AN ELECTRICALLY DRIVEN FAN FOR DIRECTING A STREAM OF SAID ATMOSPHERE AGAINST SAID PAD, ELECTRICALLY DRIVEN MEANS FOR MOVING SAID PAD THROUGH SAID STREAM OF ATMOSPHERE, THEREBY EXPOSING THE SURFACE OF THE PAD THERETO FOR A PRE-DETERMINED INTERVAL OF TIME, CAPILLARY MEANS FOR CONTACTING SAID PAD AND MOISTENING IT WITH A LIQUID THAT IS REACTIVE TO SAID REACTIVE AGENTS, SAID CAPILLLARY MEANS BEING LOCATED IN THE PATH OF TRAVEL OF THE PAD PRIOR AND ADJACENT TO ITS POINT OF EXPOSURE TO THE STREAM OF ATMOSPHERE, A DRYING CHAMBER LOCATED ABOUT THE PATH OF TRAVEL OF THE PAD SUBSEQUENT AND ADJACENT TO ITS POINT OF EXPOSURE TO THE STREAM OF ATMOSPHERE, AND MEANS FOR SUPPLYING A STREAM OF HOT, DRY ATMOSPHERE TO SAID DRYING CHAMBER, SUCH MEANS INCLUDING AN ELECTRICAL HEATING DEVICE AND A FILTER LOCATED IN THE PATH OF THE STREAM. 